The invention relates to a reversible cutting tip for a cutting tool comprising a cutting wedge defined by a first face and a first flank. The present invention also relates to a method for producing such a reversible cutting tip whereby the cutting tip comprises at least one first face and at least one first flank. The invention further relates to a tool furnished with such a reversible cutting tip and also to a method for cutting a workpiece by using such a reversible cutting tip or a tool provided with such cutting tips.
The movements during a cutting process are relative movements between the cutting edge of the tool and the workpiece. The movements are produced by the machine tool and can be performed linearly, circularly or in any other preferred motion. The cuttings result when the cutting wedge defined by the first flank and the first face, penetrates the workpiece by the effective cutting movement after completion of a feed movement. Cutting wedges consisting of metallic and non-metallic materials are known such as, for example, cutting steel, hard metal, ceramic materials, mixed ceramic materials, corundum, silicon carbide, boron carbide, diamond etc.
Especially hard metal cutting tips can be provided with a very thin surface layer consisting of extremely fine carbide or ceramic materials that provides a considerable increase of wear resistance. The most important coating materials which are applied by vapor deposition in vacuum are TiCN, TiN, Al2O3, and TiC. Vapor deposition of the coating materials can be performed by physical vapor deposition, chemical vapor deposition, and also arc-physical vapor deposition. Physical vapor deposition (PVD) produces maximum layer thickness of approximately 2 to 5 xcexcm, the chemical vapor deposition (CVD) produces maximum layer thickness of approximately 12 to 15 xcexcm, and the arc-physical vapor deposition (arc-PVD) produces a maximum layer thickness of up to 50 xcexcm. When the tool engages the workpiece, the cutting material or its coating is in surface contact with the workpiece along the first face. The cutting edge is subjected to a wear-inducing load by the cutting movement which results in a flattening of the edge, i.e., the so-called first face and first flank wear. The loading of the surfaces at the cutting wedge by pressure and shearing forces under increased temperature varies however. Therefore, a differentiation between different failure types of the different surface elements is made, for example, first flank wear, crater wear, plastic deformation, notch wear, crack formation, fatigue, splintering, tool breakage, built-up edge formation etc. These wear patterns can occur simultaneously and affect the cutting process and the surface quality at the workpiece. In practice, abrasive wear is acceptable for economic reasons. The length of the service life of the cutting edge is determined as a parameter of passive force, resulting heat, and surface quality. The wear by splintering of the cutting elements is, in general, defined as the end of practical service life.
The cutting wedges are, in general, produced for economic reasons only as small reversible cutting tips in order to be able to use the base body of the tool repeatedly for many service life periods of the cutting tips and in order to require only a minimal use of expensive cutting materials. At the same time, the conventional machining processes must fulfill steadily increasing requirements with regard to precision of the cutting edge (xc2x10.01 mm). When employing sintering repeatable results for multiple charges can only be achieved with additional subsequent grinding processes as a result of shrinkage. Also, high requirements with regard to the quality of the receiving elements for the cutting tips must be fulfilled because they must ensure for multiple service life periods of the cutting tips a precise positioning and securing of the reversible and exchangeable cutting tips. The exchange and attachment of the cutting tips must be performed by qualified personnel because the cleanness of the seats and the repeatable attachment movements affect the precise positioning of the cutting tip.
The cutting edge of conventional cutting tips requires a clearance angle. The constant feed continuously moves the contour produced by the cutting edge into the machining range of the tool. This process requires clearance for milling operations with parallel as well as opposite movement. The smaller the ratio of the cutting tip movement of the cutting velocity vector, the smaller the kinematic need for a clearance angle. Heat development of the workpiece material within the zone behind the cutting edge causes heat expansion and bulging of the surface of the machined workpiece. Because of the return of elastic deformations of the workpiece material by the passive force at the cutting edge, it is advantageous to have a clearance angle. The magnitude of the clearance angle is affected by the ratio of the cutting velocity to the feed velocity as well as the kinematic movement (outer or inner machining, rotating tool or rotating workpiece). For identical cutting parameters the required clearance angle increases with more closely spaced cutting tips. This is advantageous in order to achieve reduced tool change times. Furthermore, the size of the clearance angle is determined by the cutting edge radius. For machining a sensible ratio between the cutting edge radius and the thickness of the cuttings must be determined. Since the possible effective feed per time unit for milling, drilling, and broaching corresponds to the sum of the feed/tooth ration and number of teeth/tool ratio, close spacing between the cutting tips is therefore desirable for economic reasons.
It is therefore an object of the present invention to embody the cutting tip of the aforementioned kind, the method of the aforementioned kind, and the tool of the aforementioned kind as well as the cutting method of the aforementioned kind such that in a simple manner and for extended service life periods of the tool, respectively, its cutting tips a high machining precision at the workpiece can be produced.
This object is inventively solved for the cutting tip by providing at that cutting wedge a clearance angle between 0xc2x0 and approximately 3xc2x0.
In the inventive method for producing the inventive cutting tip, the first face and the first flank are respectively produced by applying at least one coating onto the cutting tip such that the clearance angle of the first flank is between 0xc2x0 and approximately 3xc2x0.
The inventive tool is characterized in that the cutting edges of the cutting tips are positioned about the circumference of the tool on an imaginary cylindrical mantle or any other suitable contour having radial symmetry.
The inventive cutting method is characterized in that the first flank is employed for smoothing the crack surface of the workpiece resulting from the removal of the cutting.
In the inventive cutting tip the clearance angle at the cutting edge is in the range of 0xc2x0 to approximately 3xc2x0. This minimal clearance angle, which can even be 0xc2x0, provides in a simple manner a reliable and satisfactory machining product. When the clearance angle is 0xc2x0, a cutting surface is provided which extends rearwardly from the cutting edge. For a sufficient stabilization of the cutting edge the portion of the cutting tip penetrating into the workpiece surface is reduced to a minimum.
The inventive method allows the production of the cutting tip in an inexpensive and simple manner. The first face, respectively, the first flank are produced at the cutting tip by applying a coating. This is possible in a simple manner. The cutting elements provided within the respective coatings can be selected according to the desired machining action to be performed with the cutting tip and according to the resulting load forces.
The inventive rotary tool has the cutting edges of the cutting tips positioned about the circumference of the tool on an imaginary cylindrical mantle or any other suitable contour of radial symmetry.
When employing the inventive tool for machining or cutting, respectively, when employing the inventive cutting tips, the first flank will smooth the crack surface at the workpiece directly after removal of the cutting from the workpiece. In this manner, it is possible to perform roughing and smoothing in a single working step. The smoothing effect eliminates the rough peaks within the crack surface of the workpiece resulting from removal of the cutting so that a subsequent finish machining or post-machining of the workpiece is no longer required.